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Deadly Burping Lakes

Alright, I do admit that the title sounds a little silly, but allow me to explain. In 1986, 1700 people and were killed when Cameroon’s Lake Nyos emitted a giant ‘burp’ of carbon dioxide. The event was so unlike anything the scientific community had previously seen that it took nearly a decade and a half to decide what had really happened and how to prevent it from occurring in the future. Or course, the idea of lakes emitting carbon dioxide is not in itself particularly surprising. What was exceptionally unusual in the case of Lake Nyos was just how gas was released and how suddenly.

So, what exactly happened? Let’s start with the ‘where’. Lake Nyos occupies the crater of an active volcano. While the volcano itself has not erupted in some time, it does release gases and in particular carbon dioxide. The gas finds its way into the depths of the lake through vents and channels in the rock. In most mid-latitude lakes, natural processes allow water to mix, diluting the CO2 and releasing it over time. In the fall, as air temperatures drop, water at the lake surface cools faster than the water below and sinks. In the spring, ice melts and cold water sinks once again. But in tropical regions such as Cameroon, temperatures stay stable year-round. Without this lake ‘turnover’, there is little mixing and the carbon dioxide remains concentrated at the bottom.

So why doesn’t it just escape? Imagine for a moment a sealed can of soda. The high pressure in the can keeps the CO2 (the ‘fizz’) dissolved in the drink. If the can were clear, you wouldn’t see bubbles, just liquid. But as soon as the can is opened and the pressure released, the gas is able to escape, producing ‘fizziness’. This is why sodas are often referred to as ‘carbonated’ drinks. Back in Lake Nyos, the situation is very similar. The pressure of the water above is enough to keep the CO2 dissolved, preventing it from converting into a gas and rising to the surface. Over time, the lake depths have accumulated more and more carbon dioxide-rich water.

It’s clear that the lake itself was a ticking time bomb, but harder to say what set it off. As gas built up, the lake became more and more unstable, to the point that even a relatively small disturbance such as a rockfall could have disturbed the water enough to set the lake off. As some carbon dioxide began to bubble out, the resulting upwelling of water would have pulled more and more CO2 with it. Scientists estimate that 0.7 to 1 cubic kilometer of gas was released, forming a 35 meter (120 foot) ‘fountain’ that lasted for several hours. The resulting white cloud of CO2, heavier that the surrounding air, flowed down the mountain, suffocating people and animals within a 25 km (15 mile) radius. In some areas, where carbon dioxide concentrations were less than 15 percent, people lost consciousness and later revived. Many others were not so fortunate.

Which brings us to the final chapter of our story. How do we prevent this kind of ‘eruption’ from happening again? Since 1986, extensive research has gone into modelling the CO2 hazard and devising an appropriate solution. It is estimated that it takes only 50 years for the lake to ‘recharge’ to a ‘dangerous’ carbon dioxide level, which presents the very real risk of another catastrophic release occurring. In 2001, engineers devised a simple yet elegant solution. A floating platform was installed, with a long vertical pipe that created a direct channel for gas to rise to the surface. This outlet has allowed a ‘ventilation shaft’ for CO2 to escape in quantities low enough not to threaten surrounding communities. To this day, the pipe continues to operate, powered only by the natural pressure of the water and buoyancy of the gas, much like a never-ending fountain of champagne.

This has been your daily dose of mostly harmless science.

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8 responses to “Deadly Burping Lakes”

This is an excellent exposition of something that had actually been worrying me ever since I heard of the 1986 emission from Lake Nyos. So now to find that there has been such ‘a simple yet elegant solution’ is very pleasing. Always good to get rid of a nagging anxiety, even if it was buried at the back of my head. BTW, thanks for visiting my blog. You have an excellent blog here, and now feel bound to follow.